The present invention relates to a carburetor having an accelerator pump, and more particularly, to an accelerator pump assembly including an accelerator pump cap, or cover.
A conventional motorcycle carburetor includes a main body or housing having an induction passage with a throat, or venturi, located intermediate the ends of the induction passage. A butterfly valve assembly or the like is mounted in the manifold end of the induction passage and controls the flow of air therethrough. A fuel bowl is mounted on the bottom of the housing and is connected to the induction passage by a discharge tube. A float located in the fuel bowl controls the level of fuel in a fuel reservoir of the fuel bowl to maintain a ready supply of fuel in the carburetor. When air flows through the throat of the carburetor, fuel is pulled from the fuel reservoir into the air stream in the induction passage of the carburetor due to the difference of pressure created by the air flow.
An increase in fuel flow is required to smoothly accelerate an engine. Typically, when a throttle is opened, airflow will increase immediately. However, an increase in the flow of fuel such as gasolene, which is denser than air, will take time to catch-up with the increased airflow. This results in a lean air-fuel mixture for an initial few moments after a call for acceleration and can cause the engine to hesitate. This problem can be overcome with the use of an accelerator pump which is typically built into the side or bottom of the carburetor. The accelerator pump functions to immediately deliver a spray of fuel to the throat of the induction passage of the carburetor to momentarily increase the fuel-to-air concentration during an initial call for acceleration.
FIG. 1 illustrates an example of a conventional accelerator pump assembly 10 that has a diaphragm 12 seated within a pump cap, or cover, 14. The cap 14 defines a chamber 16 that fills with fuel from a fuel reservoir 18 of the fuel bowl via a normally-opened check-valve 20. When the accelerator pump is actuated, a push rod 22 causes the diaphragm 12 to deflect downwardly thereby pumping fuel in chamber 16 through a normally-closed check-valve 24 through an outlet passage 26 and to a nozzle located in the induction passage of the carburetor downstream of the venturi. Check-valve 20 closes when the diaphragm pumps fuel and opens thereafter to refill chamber 16 with fuel.
A problem experienced with known accelerator pump assemblies is that vapor and gas can collect within the chamber of the pump. The presence and continued collection of vapor within a pump assembly can reduce engine response during start-up and acceleration. For example, when the accelerator pump is actuated, the vapor or gas within the chamber becomes compressed and fuel delivery is delayed. Thus, there is a need for an accelerator pump that reduces and/or prevents vapor and/or gas collection in the chamber of the pump.